Identification of an extracytoplasmic function sigma factor that facilitates c‐type cytochrome maturation and current generation under electrolyte‐flow conditions in Shewanella oneidensisMR‐1

Abstract

Shewanella oneidensis MR-1 was cultured on electrodes in electrochemical flow cells (EFCs), and transcriptome profiles of electrode-attached cells grown under electrolyte-flow conditions were compared with those under static (nonflow) conditions. Results revealed that, along with genes related to c-type cytochrome maturation (e.g., dsbD), the SO_3096 gene encoding a putative extracytoplasmic function (ECF) sigma factor was significantly upregulated under electrolyte-flow conditions. Compared to wild-type MR-1 (WT), an SO_3096-deletion mutant (ΔSO_3096) showed impaired biofilm formation and decreased current generation in EFCs, suggesting that SO_3096 plays critical roles in the interaction of MR-1 cells with electrodes under electrolyte-flow conditions. We also compared transcriptome profiles of WT and ΔSO_3096 grown in EFCs, confirming that many genes upregulated under the electrolyte-flow conditions, including dsbD, are regulated by SO_3096. LacZ reporter assays showed that transcription from a promoter upstream of dsbD is activated by SO_3096. Measurement of current generated by a dsbD-deletion mutant revealed that this gene is essential for the transfer of electrons to electrodes. These results indicate that the SO_3096 gene product facilitates c-type cytochrome maturation and current generation under electrolyteflow conditions. The results also offer ecophysiological insights into how Shewanella regulates extracellular electron transfer to solid surfaces in the natural environment.

Comparative Genomic Analysis of the DUF34 Protein Family Suggests Role as a Metal Ion Chaperone or Insertase

“…More recently, refute of the protein's involvement in metal ion tolerance has led to predictions of CutA1 proteins acting in a small molecule carrier or signaling capacity [154,155]. Still, the functions of all three "CutA" proteins remain under-defined with only small attributions put forward for each, in addition to CutA1: CutA2 (DsbD) is thought to have disulfide oxidoreductase activity [156]; and CutA3 (YjdC) has been annotated as an HTH-type transcriptional regulator (TetR/AcrR family), more specifically a negative regulator of nitroreductase NfnB [157]. S5 for categories and respective COG designations/InterPro signature profiles in tabular format.…”

Shewanella oneidensis MR-1 as a bacterial platform for electro-biotechnology

“…It is also noteworthy that an MR-1 mutant that does not synthesize cell-surface polysaccharides is more adhesive to electrodes than the wildtype and generates more current [50]. A recent work has conducted transcriptomic analyses of EABFs for gaining insights into molecular mechanisms behind EABF formation by MR-1 under electrolyte-flow conditions, suggesting the involvement of several yet-unidentified global regulators, including those categorized into an extracytoplasmic function sigma factor and a diguanylate synthase [51]. A subsequent study has shown that the diguanylate synthase is involved in regulating the global level of cyclic-di-GMP (c-di-GMP) in MR-1 cells and facilitating biofilm formation on electrodes [52].…”

Comparative Genomic Analysis of the DUF34 Protein Family Suggests Role as a Metal Ion Chaperone or Insertase

“…More recently, refute of the protein's involvement in metal ion tolerance has led to predictions of CutA1 proteins acting in a small molecule carrier or signaling capacity [155,156]. Still, the functions of all three "CutA" proteins remain under-defined with only small attributions put forward for each, in addition to CutA1: CutA2 (DsbD) is thought to have disulfide oxidoreductase activity [157]; and CutA3 (YjdC) has been annotated as an HTH-type transcriptional regulator (TetR/AcrR family), more specifically a negative regulator of nitroreductase NfnB [158]. clade of Viridiplantae with the closest incidence of homologs occurring in select haptophyta.…”